"I do not expect, nor do I want any of you to miss or sacrifice important family obligations for work. Family obligations include, but are not limited to family birthdays, anniversaries, weddings, any religious ceremonies such as first communions and bar mitzvahs, graduations and times of need such as an illness or a loss in the family," Biden wrote.

"This is very important to me," the letter said. "In fact, I will go so far as to say that if I find out you are working with me while missing important family responsibilities, it will disappoint me greatly. This has been an unwritten rule since my days in the Senate."

Writer Scott Smith posted the image on Twitter, and it quickly went viral.

Comparisons were quickly drawn to a tweet from Donald Trump Jr., the son of Republican presidential nominee Donald Trump.

"At dinner (with) our greenskeeper, who missed his sister’s wedding (to) work," the younger Trump wrote in 2012. "No big deal. Hopefully she’ll have another someday." Trump also said he loved the landscaper's "loyalty" to the Trump family.

Throughout his political life, Biden has remained devoted to his family. In May 2015, his son, former Delaware Attorney General Beau Biden, died after suffering from brain cancer.